Method for manufacture of surface modified thermoplastic fibers and filaments



Jan. 27, 1970 J. H. SANDERS EFAL 3,492,142

METHOD FOR MANUFACTURE OF SURFACE MODIFIED THERMOPLASTIC FIBERS AND FILAMENTS Filed June 28, 1965 INVENTORS. John H- Sanders Ruperf B. Hurley wzz/daw HTTORNEY-S United States Patent 3,492,142 METHOD FOR MANUFACTURE OF SURFACE MODIFIED THERMOPLASTIC FIBERS AND FILAMENTS John H. Sanders, Newport News, and Rupert B. Hurley, Wiliiamsburg, Va., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed June 28, 1965, Ser. No. 469,969 Int. Cl. C08d 13/16; B44d N07 US. Cl. 1179 Claims ABSTRACT OF THE DISCLOSURE Thermoplastic filaments having a non-lustrous appearance and a permanent wool-like hand are prepared by a method comprising the steps of (l) applying to a thermoplastic filament while it is in a deformable condition an aqueous dispersion of finely divided particles of a compatible thermoplastic polymer so as to cause the particles to adhere to the surface of the filament and (2) dryingthe' filament at an elevated temperature to an integral composite filament comprised of the substrate and a multiplicity of protrusions from the surface developed by the discrete polymer particles firmly bonded about the filament surface.

This invention relates to a method for the preparation of synthetic thermoplastic polymeric fibers and filaments having modified surface characteristics.

It is well known that most of the man-made fibers including the generic classes of nylons, polyesters, acrylics and polyolefins have a rather smooth, lustrous or shiny appearance and frequently a rather slick or greasy feel or hand. For many purposes, it is desirable to have a non-lustrous fiber and one without the slick feel or hand. For that-matter, great efforts and pains are generally resorted to in order to provide such fibers, particularly for apparel end use, with a wool-like hand. Wool, of course, is possessed of an inherent rough surface (When viewed under a microscope) and provides a hand we have become accustomed to and would like to have in many of the synthetic fibers.

Probably the most frequently employed methods to impart a wool-like hand in synthetic fibres (and to assist in processing synthetic fibers on conventional woolhandling textile equipment) are the large class of treatments referred to in the trade as texturizing treatments. Texturizing includes such treatments as crimping, drawing the fibers over a sharp edge, bulking and entangling the filaments by passing a bundle of them through an air jet, etc. While such treatments have received wide acceptance, certain drawbacks are attendant their'use. For instance, frequently the texturizing treatment does not have a lasting effect, and moreover, often a reduction or adverse alteration of otherwise desirable :fiber'physical properties is encountered. In US. 2,736,946

a means is suggested for providing acrylonitrile polymer fibers with a wool-like hand (which is therein referred to as a scaly integument) which involves an abrupt coagulation technique which breaks up the surface of the fiber over a solid core. However, this method also tends to impair fiber physical properties. In U.S. 3,180,- 785 fibers are discussed having an irregular distribution of flat prismatic crystals on the fiber surfaces which are developed from within the fiber by the heat treatments. However, not all fibers are susceptible of such crystal growth and the surface may be too snaggy for many textile processes.

Accordingly, it is an object of the present invention to provide synthetic polymeric filaments having modified 3,492,142 Patented Jan. 27, 1970 Ice surface characteristics and improved aesthetic properties without substantially affecting the filament physical properties. It is a further object to provide synthetic polymeric filaments having unique dyeing and other properties. It is yet a further object to provide a means for manufacturing synthetic polymeric filaments having modified surface characteristics so as to impart to them a wool-like hand and other unique and beneficial characteristics.

The foregoing and additional objects and cognate benefits and features are accomplished in and by practice of the present invention which comprises applying to a thermoplastic filament substrate while it is in a plastic or deformable condition an aqueous dispersion of finely divided particles of a compatible thermoplastic polymer so asto cause the particles to adhere to the surface of the substrate, said particles having been prepared by polymerizing the monomeric material of which said polymer particle is comprised in an aqueous nonpolymer dissolving medium, and then drying the filament at an elevated temperature to an integral composite filament comprised of the substrate and a multiplicity of protrusions from the surface developed by the discrete polymer particles firmly bonded about the substrate surface. Provided by this means is a filament having an irregular woollike fiber surface.

The present invention has as a primary advantage the provision of thermoplastic filaments having a generally non-lustrous appearance and wool-like hand. As has been indicated, fibers with such characteristics are met with high acceptance in the apparel industry. It will be appreciated by the artisan that the foregoing benefits can be realized by practice of the invention without significant depreciation of the inherent physical properties of the substrate filament. Among the other beneficial features of the invention, which will be apparent to the artisan, are the numerous novel and unique characteristics that can be built-in to the instant composite filaments. Thus, by way of example, particles of a different composition than the substrate can be employed. This can lend distinct lustrous and iridescent effects. The particles and substrate can be of different colors to provide unusual effects. Additionally, when different compositions are employed they will generally dye to different shades of coloration which leads to numerous possibilities. Of course, where a particular polymer composition is desired, the discreteparticles and substrate polymer are of the same polymeric composition.

Developing the particles by means of suspension polymerization (or slurry, dispersion or emulsion polymerization) provides particles that are uniformly pre-sized (by controlling the polymerization reaction). Additionally, particles of exceptional fineness can be had without the great expense of grinding and sizing. For that matter some of the thermoplastic materials, because of their relative resiliency, are very difficult to size by grinding. As an additional useful feature, the particles so obtained are generally round smooth-surfaced and do not present sharp or ragged edges that may induce snags and the like when the fibers are employed. The aqueous media employed are also very easily handled and avoid fire and the like hazards.

An example of the composite filaments provided by the present invention is shown in the photomicrographs of FIGURES l and 2. FIGURE 1 is a photomicrograph (magnified 10,000 of the surface of a composite filament provided by the present invention. FIGURE 2 is a photomicrograph (magnified 164,000X) of a cross-section of a composite filament provided by the present invention.

The filament substrates can be of any normally solid fiber-forming thermoplastic polymer which can be shaped by any of the conventional fiber-spinning techniques. Thus, exemplary of the polymers of which the substrate filament may be constituted include cellulose esters, e.g.,

cellulose acetate, propionate, butyrate, etc. polyamides, e.g., nylon 6, i.e., polymerized epsilon caprolactam, nylon 66, i.e., a polymer from adipic acid and hexamethylenediamine; polyacrylics, e.g., acrylonitrile polymers; polyesters, e.g., polyethylene glycol terephthalate; polyolefins, e.g., polyethylene, polypropylene, copolymers of ethylene and propylene, and so forth; vinyl and vinylidene chloride polymers and similar polymeric materials that are adaptable to be fabricated into filamentary shapes.

Any of the foregoing and related polymers can also be employed in the preparation of the particles that are appended to the surface of the substrate filament.

As indicated, any combination of a thermoplastic polymer and a thermoplastic particle can be combined in the present composite filaments. However, for practical reasons, it is advantageous if the substrate filament and particle are of a compatible thermoplastic polymer. That is, that the compositions are such that the particle will become firmly bonded to and in the surface of the filament. The degree of bonding desired will depend in part upon the end use designed for the composite filament. Usually a secure and permanent bond is desired since the filaments will usually be subjected to rather severe processing treatments such as may be encountered in a textile mill or dyehouse or the like. It is further to be realized that the composite filaments of the present invention are held together solely by the self-bonding of the polymers of the respective filaments and particles. No adhesives or bonding agents are employed. These are to be avoided since their use complicates the fabrication of the composite articles and requires additional treatments and bandling of the materials adding to the cost and mess of the fabrication. Also, it is generally observed that adhesives and bonding agents are not particularly permanent over a long period of time and particularly when subjected to such severe treatments as dyeing and scouring and the like. Moreover, such agents may leach out from the fiber and cause irritation to the wearer of apparel made from such filaments as well as to change the hand of filaments and fabrics made therefrom. Advantageously and beneficially, in the practice of the present invention, the filaments and particles of the composite filaments are of the same polymeric material and preferably have essentially the same molecular weight. This combination usually provides excellent and permanent bonding between the particle and the substrate filament.

With reference to FIGURE 1, it can be seen that the particles on the filament surface retain for the most part their individual identity. While frequently a large number of the particles may be agglomerated so as to be bonded or fused in side-by-side relationship to one another, the identity of the individual particles, at least that portion protruding above the surface of the filament, remains apparent. This arrangement is desirable inthe practice of the present invention so as to provide to the surface of the filament the roughened character providing a wool-like hand.

Generally, the composite filaments are preared so as to be comprised of a minor amount of the particles, the major proportion of the composite filament being made up of the substrate filament. However, the composite filaments can be made up from about 1 to 50 Weight percent of the particles with the remainder being the substrate filament. Preferably, between about 5 and weight percent of the particles are applied to the substrate filaments.

Advantageously, the size of the particles employed in the present invention have a diameter of from about 0.1 to 10 microns and preferably from about 0.1 to 1 micron. In any event, the particles have a diameter substantially less than the diameter of the substrate filament upon the surface of which they become appended. For example,

an average size textile filament is generally from about 2 to 1,5 denier corresponding to a diameter of about 18 to 42 microns. Accordingly, it can be seen that the indicated desirable size of the particles are substantially less than the filament diameter.

As indicated, the particles are applied to the filament from an aqueous dispersion of the particles. This dispersion or emulsion is applied to the substrate filament while applying to the filament a pressure sufiicient to cause the particles to become at least partially embedded in the surface of the filament. While several means can be employed to this end, advantageously the dispersion of emulsion is padded onto the filament surface. Conventional padding equipment can thus be utilized which, of course, involves generally a pair of nip rolls immediately following or immersed in the dispersion or emulsion as well as other alternative arrangements.

A uniform dispersion is desirable from the standpoint of assuring relatively uniform contacting of the filament surface with the particles. However, uniformity of distribution of the particles on the filament surface is by no means a necessity in the practice of the present invention. For that matter, a more or less random distribution is preferable from the standpoint of providing a more roughened surface thus simulating the surface of a wool fiber. As indicated, the dispersions of particles are prepared by polymerizing the monomer from which the polymer particle is constituted in an aqueous nonsolvent for the particle. This is generally referred to as suspension or emulsion or slurry polymerization wherein the polymer comes out of solution during the polymerization of monomer and provides a separate phase. Ordinarily, various emulsifying and suspending agents are employed in such polymerization techniques to assist in maintaining a uniform dispersion or emulsion and to prevent the polymer particles from precipitating from the polymerization medium. In this connection, the particle size, which can be very small, can be quite carefully controlled by controlling the polymerization reaction by known means.

In order to provide a secure bond between the particle and the substrate filament, the filament should be in a deformable, swollen or p'lasticized condition so that when the polymer particle is pressed against it during the application of the particle, the particle becomes at least partially embedded in the surface of the filament. In other words, the filament should be in a reduced resilient state so as not to spring back after the particle 'is applied thereto and thus push the particle off from the surface. By a reduced resilient state is meant that it is substantially less resilient than a filament that has been dried to a characteristic textile filament. Thus, normally synthetic thermoplastic filaments employed in the textile trade normally have a relatively resilient and somewhat hard and glossy surface.

In order to provide the filaments in such a deformable or plasticized condition, filaments can be employed containing a plasticizer which causes the filaments to have a pliable and deformable surface. Advantageously, when a plasticizer is employed, it is of the fugitive type which can be readily removed from the fiber during the drying operation at elevated temperatures. The filament can also be heat softened and thus receptive to the embedding therein of the particles in accordance with the invention. One means that is particularly advantageous is to apply the dispersion of particles to the filaments immediately after they have been fabricated by heat-fabrication techniques. For example, after a filament is melt spun from a molten mass of the polymer and before the filament iscooled to a normally solid state is an advantageous time to apply the particles thereto. Or, when filaments are dry spun, i.e., spun from a solution of the polymer in a volatile solvent, the particles can be applied to the filaments while the filaments still contain a portion ofthe volatile solvent which acts as a plasticizer and presents the fibers in a deformable condition.

The invention is especially adapted to the application of the particles to filaments that are wet spun from a solution of the polymer. Normally, when such wet spinning techniques are followed, a solution of the polymer is spun into a coagulation bath, which is frequently an aqueous coagulation bath, and the fiber on emerging from the coagulation bath is in a gel or highly swollen condition. While the fiber is in this gel condition, it is exceptionally deformable and especially suited for the application thereto of a dispersion of the indicated particles. This combination provides exceptional results in that the inert medium of the emulsion or dispersion and the inert medium in the aquagel fiber are compatible and present no problems regards interaction or later recovery in the separtaion of liquids. Acrylonitrile polymer gel or aquagel filaments are particularly Well suited for employment in the instant invention.

It is, of course, to be realized that some filaments are benefited more than others due to the fact that some filaments have what might be termed, by comparison, a rough surface as initially prepared, whereas others are extremely smooth. For example, it has been observed that acrylonitrile polymers that are spun from an aqueous zinc chloride solution into an aqueous about 43 weight percent zinc chloride coagulation bath at about C. have a somewhat rough surface. In contrast, such polymer solutions spun into a coagulation bath having a zinc chloride concentration from about 30 to 36 weight percent have a slick smooth surface. Filaments prepared under these latter spinning conditions are exceptionally benefited by the practice of the present invention.

After the particles have been applied to the surface of the deformable substrate filament, the filament is dried at an elevated temperature to a characteristically hydrophobic textile fiber. The drying conditions should be such as to volatilize and remove from the composite filament any of the residual inert mediums in the substrate filament or particle but not so great as to cause any flowing of the polymer in the filament so as to substantially change the cross section of the substrate filament. Drying under these conditions induces a permanent bond, generally by fusion, between the particle and the substrate filament and also frequently causes side-by-side fusion of the individual particles. However, as indicated, the particles still, and the conditions should be such as to provide the particles upon the filament surface to, retain a substantial individual identity. Also, the particles, as has been indicated, should be caused to protrude substantially above the surface of the substrate filament.

In order to further illustrate the invention, a 10% by weight solution of a terpolymer (91% acrylonitrile, 7.5% methyl acrylate, 1.5% sulfoethyl acrylate) in an aqueous about 60 weight percent ZnCl solution was extruded through a 100-hole spinnerette, such holes being about 3 mils in diameter, into an aqueous coagulation bath of about 32.5 Weight percent zinc chloride maintained at about 30 C. The coagulated filaments were washed and stretched 8.5x in boiling water. A by weight aqueous, emulsion-polymerized dispersion of polyacrylonitrile, having a particle size of about 0.8 micron, was padded onto the wet stretched aquagel, resulting in a pickup of about 8% emulsion particles by Weight on the fibrous filaments. The tow was then dried in an air circulating oven at a temperature of 130 C. for five minutes. The resultant fiber had a crisp hand similar to wool and a surface similar to that shown in the photomicrographs of FIGURES 1 and 2. In contrast filaments prepared according to the foregoing but which had no application of the particle emulsion had a slick smooth surface, and when viewed microscopically were observed to have a smooth surface.

Similar excellent results to the foregoing are achieved in and by the practice of the invention when other polymeric filaments and other polymeric particles are employe'd.

What is claimed is:

1. The method of preparing an oriented filament of an acrylonitrile polymer, said filament having a non-lustrous appearance and a permanent wool-like"hand comprising, providing a filament in a gel condition by wet spinning a filament from a solution of an acrylonitrile polymer such that the surface thereof is deformable and in a reduced resilient state in comparison to its normal state after it has been dried to a characteristic textile filament, applying to the gel filament an aqueous dispersion of discrete, minute solid particles of an acrylonitrile polymer while exerting pressure against the surface of said gel filament, said particles having been prepared by polymerizing the monomeric material of which said polymer is comprised in an aqueous non-polymer dissolving medium, and subsequently drying said gel filament at an elevated temperature to provide a composite filament having a filament substrate and at least partially embedded in the surface thereof a multiplicity of minute particles, a substantial portion of said particles protruding above the surface of said filament, said particles adhering to said filament solely by the fusion of said particles to said filament as a consequence of drying said composite filament at an elevated temperature.

2. The method of claim 1, wherein said particles have a diameter of from about 0.1 to 10 microns.

3. The method of claim 1, wherein said particles have a diameter of from 0.25 to 1 micron.

4. The method of claim 1, wherein from about 1 to 50 weight percent, of said particles is applied to said filament, based on the dry weight of the composite filament.

5. The method of claim 1, wherein from about 5 to 15 weight percent of said particles is applied to said filament, based on the dry weight of the composite filament.

References Cited UNITED STATES PATENTS 2,628,172 2/1953 Jenett 1l7-l38.8 X 2,686,736 8/1954 Kuhn 117138.8 X 2,714,075 7/1955 Watson et al. 117138.8 X 2,859,135 11/1958 Rossin 117--138.8 X 2,862,284 12/1958 Wiczer 117138.8 X 3,122,443 2/1964 Blankenship et al. 264182 X 2,988,782 6/ 1961 Parrish et al.

3,047,426 7/ 1962 Murdock et al.

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FOREIGN PATENTS 665,029 6/1963 Canada.

WILLIAM D. MARTIN, Primary Examiner J. E. MILLER, Assistant Examiner US. Cl. X.R. 

